Wide-area motion imaging (WAMI) has received increased attention for defense and commercial applications due to the importance of wide-area persistent surveillance for homeland protection, battlefield situational awareness, environmental monitoring, and intelligence, surveillance, and reconnaissance of denied areas. Recently developed systems, such as Argus-IS, can surveil up to 100 km2 at over a gigapixel resolution from an airborne platform. This huge amount of visual data requires algorithms for automated detection and tracking of targets of interest. However, traditional kinematic data based tracking algorithms have challenges in wide area motion imagery due to a relatively low sampling rate, low spatial resolution, occlusions, changes in lighting, and multiple confusers. Incorporating hyperspectral data can boost the probability of detection, reduce false alarms, and improve performance in vehicle tracking and dismount detection.
Currently fielded imaging spectrometers use either dispersive or interferometric techniques. A dispersive spectrometer uses a grating or prism to disperse the spectrum along one axis of a focal plane array (FPA) while the other axis is used to measure a single spatial dimension. An interferometric spectrometer reconstructs the spectrum from an interferogram measured at the FPA by splitting the incident light into two optical paths and varying the optical path distance of one of the paths with a moveable mirror.
Neither dispersive spectrometers nor interferometric spectrometers are suitable for motion imaging a large area on the ground. For example, to cover 64 km2 at a ground sampling distance of 0.5 m, an update rate of 1 Hz, and up to 256 spectral bands, a dispersive grating spectrometer must sacrifice signal-to-noise ratio (SNR) (<4 μs dwell time per pixel). An interferometric spectrometer is not even capable of imaging at a 1 Hz update rate as its mirror would have to move more than an order of magnitude faster (65,000 steps/sec) than what is typically available (2000 steps/sec). Given these constraints, it is not surprising that no military or commercial WAMI platform has a hyperspectral sensing capability. Therefore, today's systems can offer large area coverage or wide spectral bandwidth, but not both.